Low specific absorption rate dual-band antenna structure

• US 9,735,822 B1
• Filed: 09/16/2014
• Issued: 08/15/2017
• Est. Priority Date: 09/16/2014
• Status: Expired due to Fees

• Current Assignee: Amazon Technologies, Inc. (Amazon.com, Inc.)
• Original Assignee: Amazon Technologies, Inc. (Amazon.com, Inc.)
• Inventors: Kuo, Jerry Weiming
• Primary Examiner(s): Nguyen, Hoang
• Assistant Examiner(s): Salih, Awat
• Application Number:
  US14/488,083
• Time in Patent Office: 1,064 Days
• Field of Search: 343741-744, 343764, 343866-867
• CPC Class Codes: H01Q 1/243 with built-in antennas
• CPC Class Codes: H01Q 1/245 with means for shaping the antenna pattern, e.g. in order to protect user against rf exposure
• CPC Class Codes: H01Q 21/30 Combinations of separate antenna units operating in different wavebands and connected to a common feeder system
• CPC Class Codes: H01Q 7/00 Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop
• CPC Class Codes: H04B 1/3838 Arrangements for reducing RF exposure to the user, e.g. by changing the shape of the transceiver while in use
• CPC Class Codes: H04B 1/40 Circuits

Abstract

Dual-band antenna structures and methods of operating the same of an electronic device are described. One apparatus includes a radio frequency (RF) feed and a dual-band antenna structure coupled to the RF feed at a feeding point and coupled to a ground plane at a grounding point. The structure includes a first loop antenna and a second loop antenna, both coupled to the feeding point and the grounding point. The first loop antenna radiates electromagnetic energy in a first resonant mode in a first frequency band and the second loop antenna radiates electromagnetic energy in a second resonant mode in a second frequency band and radiates electromagnetic energy in a third resonant mode in the first frequency band. Surface currents create a pair of hot spots of magnetic field.

Claims

1. An electronic device comprising:

a transceiver to transmit and receive radio frequency (RF) signals;

a RF feed coupled to the transceiver; and

a dual-band antenna structure coupled to the RF feed, wherein the dual-band antenna structure comprises;

a ground plane;

an outer loop structure including an outer loop element, the outer loop element coupled to the RF feed at a feeding point at a near end of the outer loop element and coupled to the ground plane at a grounding point at a distal end of the outer loop element, the distal end of the outer loop element being farther from the RF feed than the near end of the outer loop element;

an inner loop structure including an inner loop element, the inner loop element coupled to the RF feed at the feeding point at a near end of the inner loop element and coupled to the ground plane at the grounding point at a distal end of the inner loop element, the distal end of the inner loop element being farther from the RF feed than the near end of the inner loop element;

a first low band band pass filter (BPF) disposed within the outer loop structure and a first high band BPF disposed between the outer loop element and the grounding plane, the first low band BPF and the first high band BPF forming a first circuit; and

a second low band BPF disposed within the outer loop structure and a second high BPF disposed between the outer loop element and the grounding plane, the second low band BPF and second high BPF forming a second circuit,

wherein the inner loop element is disposed at least partially within an inner area defined by the outer loop element, the inner loop element configured to radiate electromagnetic energy in a first quarter-wave resonant mode in a first band of the dual-band antenna structure when the RF signals are applied to the RF feed,

wherein the outer loop element radiates electromagnetic energy in a second quarter-wave resonant mode in a second band of the dual-band antenna structure and radiates electromagnetic energy in a third three-quarters-wave resonant mode in the first band of the dual-band antenna structure when the RF signals are applied to the RF feed.

2. The electronic device of claim 1, wherein the outer loop element comprises:

a first arm portion that extends from the feeding point to a first junction in a first direction;

a second arm portion that extends from the first junction in a second direction towards a second junction;

a third arm portion that extends from the second junction in a third direction towards a third junction;

a fourth arm portion that extends from the third junction in a fourth direction towards a fourth junction; and

a fifth arm portion that extends from the fourth junction in the first direction towards the grounding point, wherein the first arm portion, the third arm portion, and the fifth arm portion are parallel to the ground plane, and wherein the second arm portion and the fourth arm portion are perpendicular to the ground plane.

3. The electronic device of claim 1, wherein the first low band BPF, the first high band BPF, the second low band BPF, and the second high band BPF each comprise at least two impedance-matching components.

4. The electronic device of claim 1, wherein the first band comprises a higher frequency range than the second band, and wherein surface currents, generated due to the RF signals being applied to the RF feed, create a first hot spot of magnetic field, proximate the first circuit, and a second hot spot of magnetic field, proximate the second circuit, the first hot spot and second hot spot each corresponding to a respective area on the dual-band antenna structure at which surface-current density is higher than on an area surrounding the respective areas of the first hot spot and the second hot spot.

5. The electronic device of claim 4, wherein the outer loop element comprises:

a first arm portion connected at the near end and extending in a first direction to a first junction;

a second arm portion connected at the first junction and extending to a second junction in a second direction;

a third arm portion connected at the second junction and extending in a third direction to a third junction;

a fourth arm portion connected at the third junction and extending in a fourth direction to a fourth junction; and

a fifth arm portion connected at the fourth junction and extending in the first direction to the distal end of the outer loop element, wherein the near end is disposed closer to the feeding point than to the first junction, the distal end is disposed closer to the grounding point than to the fourth junction, and the surface current of the RF signals creates the first hot spot near the feeding point and the second hot spot near the grounding point.

6. An apparatus comprising:

a radio frequency (RF) feed; and

a dual-band antenna structure coupled to the RF feed by a first circuit proximate a feeding point and coupled to a ground plane by a second circuit proximate a grounding point,

wherein the dual-band antenna structure comprises a first loop antenna coupled to the feeding point and the grounding point and a second loop antenna coupled to the feeding point and the grounding point, the first loop antenna configured to radiate electromagnetic energy in a first resonant mode in a first frequency band and the second loop antenna configured to radiate electromagnetic energy in a second resonant mode in a second frequency band of the dual-band antenna structure, the first frequency band corresponding to a higher frequency band than the second frequency band,

wherein the dual-band antenna structure is configured to create two hot spots, a first hot spot of the two hot spots being located proximate the first circuit, and a second hot spot of the two hot spots being located proximate the second circuit, and

wherein the dual-band antenna structure further comprises;

a first low band band-pass filter (BPF) disposed within an outer loop structure including the outer loop antenna,

a first high band BPF disposed between the outer loop antenna and the grounding plane,

a second low band BPF disposed within the outer loop structure, and

a second high BPF disposed between the outer loop antenna and the grounding plane.

7. The apparatus of claim 6, wherein the second loop antenna comprises an outer loop element comprising a near end coupled to the feeding point, a distal end coupled to the grounding point, a first junction, and a second junction, wherein the first loop antenna is disposed at least partially within an inner area defined by the outer-loop element.

8. The apparatus of claim 7, wherein surface currents applied at the feeding point create the first hot spot and the second hot spot.

9. The apparatus of claim 6, wherein the second loop antenna comprises:

a first arm portion that extends from the feeding point to a first junction in a first direction;

a second arm portion that extends from the first junction in a second direction towards a second junction;

a third arm portion that extends from the second junction in a third direction towards a third junction;

a fourth arm portion that extends from the third junction in a fourth direction towards a fourth junction; and

a fifth arm portion that extends from the fourth junction in the first direction towards the grounding point, wherein the first arm portion, the third arm portion and the fifth arm portion are parallel to the ground plane, and wherein the second arm portion and the fourth arm portion are perpendicular to the ground plane.

10. The apparatus of claim 9, wherein the first loop antenna is disposed between the first arm portion and the fifth arm portion of the second loop antenna.

11. The apparatus of claim 6, wherein the first circuit is symmetric to the second circuit, each circuit of the first circuit and the second circuit being configured to constrain current over a determined range of frequencies from leaving a respective area proximate the circuit.

12. The apparatus of claim 6, wherein the first low band BPF, the first high band BPF, the second low band BPF, and the second high band BPF each comprise at least two impedance-matching components.

13. The apparatus of claim 6, wherein the first loop antenna and the second loop are quarter-wave antennas, and wherein the first frequency band is approximately 2.3 GHz to approximately 2.6 GHz and the second frequency band is approximately 5.0 GHz to approximately 6.0 GHz.

14. The apparatus of claim 6, wherein the first resonant mode is centered at approximately 5.1 GHz and the second resonant mode is centered at approximately 2.44 GHz.

15. The apparatus of claim 6, wherein the feeding point and the grounding point are at least 5 mm apart.

16. A method of operating an electronic device, the method comprising:

applying a current to a radio frequency (RF) feed coupled to a dual-band antenna structure to transmit RF signals in a first frequency range and a second frequency range, the dual-band antenna structure being coupled to the RF feed by a first circuit proximate a feeding point and coupled to a ground plane by a second circuit proximate a grounding point, wherein the current applied to the RF feed creates surface currents on the dual-band antenna structure, wherein the dual-band antenna structure comprises a first loop antenna and a second loop antenna;

creating, by the dual-band antenna structure, a first hot spot of magnetic field proximate the first circuit when the current is applied to the RF feed; and

creating, by the dual-band antenna structure, a second hot spot of magnetic field proximate the second circuit when the current is applied to the RF feed, wherein;

the first circuit comprises;

a first low band band-pass filter (BPF) disposed within an outer loop structure including the outer loop antenna, and

a first high band BPF disposed between the outer loop antenna and the grounding plane, and

the second circuit comprises;

a second low band BPF disposed within the outer loop structure, and

a second high band BPF disposed between the outer loop antenna and the grounding plane.

17. The method of claim 16, further comprising:

upon applying the current,

radiating, by the dual-band antenna structure, electromagnetic energy in a first resonant mode in a first frequency range;

radiating, by the dual-band antenna structure, electromagnetic energy in a second resonant mode in a second frequency range, and

radiating, by the dual-band antenna structure, electromagnetic energy in a third resonant mode in the second frequency range.

18. The method of claim 17, wherein the first frequency range is approximately 2.3 GHz to approximately 2.6 GHz and the second frequency range is approximately 5.0 GHz to approximately 6.0 GHz.

19. The method of claim 17, wherein the first resonant mode is centered at approximately 5.1 GHz, the second resonant mode is centered at approximately 2.44 GHz, and the third resonant mode is centered at approximately 5.6 GHz.

20. The method of claim 17, wherein the radiating the electromagnetic energy in the second resonant mode and in the third resonant mode comprises radiating, by the second loop antenna, electromagnetic energy in the second resonant mode and in the third resonant mode.